Open-string boundary condition in a B-field
= Open-string boundary condition in a B-field
For a D-brane in metric $G$, pulled-back B-field $B$ and worldvolume field strength $F$, tangential open-string coordinates obey the mixed condition $G_{ab}\partial_\sigma X^b+(B+2\pi\alpha'F)_{ab}\partial_\tau X^b=0$. Only the gauge-invariant combination $B+2\pi\alpha'F$ is physical.